Communication networks typically operate in accordance with a given standard or specification which sets out what the various elements of the network are permitted to do and how that should be achieved, i.e. the technology on which the communication is based on in the network. The standard may define whether a user of the system or more precisely, a user equipment is provided with a circuit switched service and/or a packet switched service. The standard may also define the communication protocols which shall be used for the connection. One or more of the required connection parameters are also typically defined. In other words, the standard defines the “rules” and parameters the on which the communication within the communication system can be based on. Examples of the different standards and/or specifications defining communication technologies include, without limiting to these, specifications such as GSM (Global System for Mobile communications) or various GSM based systems (such as GPRS: General Packet Radio Service), EDGE (Enhanced Data rate for GSM Evolution), AMPS (American Mobile Phone System), DAMPS (Digital AMPS), WCDMA (Wideband Code Division Multiple Access) or CDMA (Code Division Multiple Access) or TDMA (Time Division Multiple Access) based 3rd generation (3G) telecommunication systems. Examples of the 3G systems include Universal Mobile Telecommunication System (UMTS), i-Phone and IMT 2000 (International Mobile Telecommunication System 2000).
User equipment, such as a fixed line or wireless terminal, that is to be used for communication over a particular communication network has to be implemented in accordance with the predefined “rules” of the network. A terminal may also be arranged to be compatible with more than one technology, i.e. the terminal may communicate in accordance with several different types of communication services. These user equipment are often called as multi-mode terminals. The basic example of the multi-mode terminals is a dual-mode mobile station arranged to operate in two different telecommunications networks.
A communication network is a cellular radio network consisting of cells. In most cases the cell can be defined as a certain area covered by one or several base transceiver stations (BTS) serving user equipment (UE) via a wireless interface. The wireless interface may sometimes be referred to as a radio link. The base station forms a part of an radio access network (RAN). Several cells may cover a larger service area than one cell. In the circuit switched (CS) systems the radio service area is typically referred to as a location area (LA). In the packet switched (PS) systems the service area is often referred to as a routing area (RA). It should be appreciated that the size of the location area or routing area depends on the system and circumstances, and may equal to one cell or be even smaller, such a part of a coverage area of a base station.
The user equipment (UE) within one of the access entities (such as the cells) of the cellular system may be controlled by one or several controllers. Examples of the controller nodes include radio network controllers such as a base station controller (BSC) of the GSM system or a radio network controller (RNC) of the packet switched 3rd generation systems and core network controllers such as a mobile switching center (MSC) of the GSM system and a serving GPRS support node (SGSN), but other control nodes may also be implemented in the network. The controller can be connected further to a gateway or linking node, for example a gateway GPRS support node (GGSN) or gateway mobile switching center (GMSC), linking the controller nodes to other parts of the communication system and/or to other communication networks, such as to a PSTN (Public Switched Telecommunications Network) or to a data network, such as to a X.25 based network or to an IP (Internet Protocol) based network. The network may also include nodes for storing information of mobile stations subscribing the network or visiting the network, such as appropriate home location registers (HLR) and visitor location registers (VLR). Depending the implementation, the register nodes may be integrated with a control node.
When user equipment communicates with a communication network, a communication path has been established between the user equipment and one or more of the elements of the network. Typically at least a part of the communication between the user equipment and a destination node or terminal then pass through the controller node.
A feature of the cellular system is that it provides mobility for the mobile stations, i.e. the mobile stations are enabled to move-from a location area to another (e.g. when the mobile station moves i.e. roams from a cell to another cell) and even from a network to another network that is compatible with the standard the mobile station is adapted to. In order to be able to provide the mobility for user equipment with an ongoing (active) connection, the system needs to be capable of accomplishing a handover of the connection from a node thereof to another node. The handover of the connection may also be required for other reasons, such as when the quality of the packet switched connection drops below a predefined threshold level or when the cell becomes too congested.
The handover should also be possible between two nodes that belong to different networks. If the new cell is not served by a similar system as the previous cell, then handover needs to be accomplished between communication systems that are based on different communication technologies. A simultaneous handover of a packet switched connection and a circuit switched connection from a terminal may also be required in some occasions.
When a handover is to be accomplished between nodes of different communications systems (i.e. systems that are based on different communication technologies), it is possible that the “new” connection cannot be properly set-up due to differences in the operation of the various elements of the “new” (i.e. target) and the “old” (i.e. previous) communication systems. For example, if a packet data communication handover is to be accomplished between two different packet data networks, such as from a third generation UMTS network to a GSM based second generation GPRS network, the user equipment (e.g. a Class B mobile station) may not be guaranteed to perform an immediate routing area update (RAU) with the controller of the new network, such as a 2G-SGSN (2nd generation SGSN) of the GPRS network. However, the radio network controller resources, like the RNC context and Iu bearers in the UMTS, may not be released in the old controller until the user equipment performs said routing area update (RAU) with the target (i.e. new) SGSN in the GPRS network. At an intersystem change from the UMTS to-the GPRS an appropriate element of the UMTS system (e.g. a 3rd generation 3G-SGSN node) releases the controller entity and Iu interface only after the user equipment has generated and send-the RAU request message. In the GSM based systems the routing area update (RAU) may be performed only after the circuit switched (CS) call is finished (i.e. the circuit switched connection is released). In addition, the 2nd generation SGSN may not be able to remove the Iu resources between the radio network controller and the 3rd generation SGSN, since the 2nd generation SGSN may not have an Iu interface or a capability to control any Iu interfaces. Therefore, it may take a substantially long period of time before the RAU procedure is completed. All that time the old RNC needs to-keep the resources reserved by the packet switched connection (e.g. Iu and RNC contexts). If the routing area update is not performed immediately, these resources are unnecessarily maintained and may thus be wasted for a substantially long period of time.